Kenny Nelson's WOPL 400 conversion.

[jbeckva]

Lickety Sp;lit is back. Shipping caused the allen head hold down screws to rattle loose and they then laid in amongst the back wall bussa bars and it got plugged in. Lights lit, 15.52 vilts DC on the outputs, no relay click, no burnt fuse, no burnt output, no burnt driver, hell, no burnt semi-conductor anywhere. R2R, R2L measured 656K, and 2 megohms. That's what burnt.

I'm STALKING you...



LOL.. anywhoo.. hmmm... So in the other thread you said R2 was smoking out every time you replaced it? Or am I confused... What's the regulated +/-20 look like on the WO board?

 

[jbeckva]

Another "check" to "check out" - Pop out the rail fuses... check for any shorts to the chassis (go along the cases of the TO-3's.. should be meg ohms.. if anything at all).

Something along the ground scheme... how else could there be current through the R2's, hmmmm...

 

[laatsch55]

OK Jer, will do. I've blown 4 pairs now...

 

[Gepetto]

Do you still have a good ground wire from pin 5 of the board to star ground Lee?

When you have R2L/R out of the circuit, do you measure high resistance between the 2 grounds? Do you measure high resistance between pin 2 of the board and the chassis when R2L/R is out of the circuit? In both cases, you should.

Is the bridge rectifier still good?

 

[laatsch55]

Joe, I have 2 separate groinds to the board, they are intack and exhibit no resistance. BR is good, haven't btried the otherr measurements yet Joe , but with the leads accross where R2 was when out of circuit it was around 200-300K.

 

[laatsch55]

Joe when it starts to go south, on the scope it looks like a severe clip on both positive and negative halves, starts drawing a lot of current also.

 

[laatsch55]

With one leg of R2 lifted, between pin 2 (rca ground) to star ground---over 200K.

 

[laatsch55]

When you have R2L/R out of the circuit, do you measure high resistance between the 2 grounds?



Do you mean between 5L, 5R??

 

[laatsch55]

Right channel is good , loaded at 8 ohms to over 300 watts, no funny stuff. he left however gives a pretty wicked waveform..... If anyone knows what causes a waveform to look like this, please post, I don't have a F&^%$# clue!!

 

[Gepetto]

Right channel is good , loaded at 8 ohms to over 300 watts, no funny stuff. he left however gives a pretty wicked waveform..... If anyone knows what causes a waveform to look like this, please post, I don't have a F&^%$# clue!!

Hi Lee
the upper half of the bridge is ununstable. I have seen this with compromised output devices as well as bad Zoebel networks

 

[Gepetto]

Hi Lee
the upper half of the bridge is ununstable. I have seen this with compromised output devices as well as bad Zoebel networks

Also check the bootstrap capacitor C11

 

[laatsch55]

Thanks Joe. If an output, will they check OK on the diode test ? Or will this be a replace one at a time and scope again?

 

[laatsch55]

C11 sounds plausible too as there seemed to be some cyclical stuff going on at times.

 

[speakerman1]

Have you heard from Ken?

 

[Gepetto]

since it is one channel Lee, I would strip the outputs down to the RCA410 level and go from there.

 

[jbeckva]

How did we get from blowing R2's to this? What'd I miss?

 

[Gepetto]

Also check for punctured insulator, high impedance short to ground. That type of thing could explain your blown R2 experience, which I think you said was both channels.

Good to know those resistors double as fuses Any obvious thermal damage to the resistors when they open up?

 

[Gepetto]

I had been considering reducing the size and wattage of R2 (down to 1/8W from 1/4W) some months ago.

 

[jbeckva]

I'm assuming the cause of R2's blowing was found?? How'd we get from there to testing the output (with osc in one channel)?

 

[Gepetto]

Perhaps Jer, I was still thinking that Lee thought them inter related.

Lee will have to advise us.